But the Kentucky duo's relationship is deeper than what happens on the Senate floor.

While Paul has dreams of the White House, McConnell is building two legacies: One in the Senate and one as an architect of the Kentucky Republican Party.

“Up until now, it’s probably been a strategic alliance that’s been mutually beneficial,” said Scott Lasley, an associate professor in the department of political science at Western Kentucky University and a central committee chairman of the state Republican Party.

Paul’s endorsement of McConnell during last year’s re-election was particularly valuable in limiting intraparty fire that could have turned on McConnell, Lasley said.

Paul, on the other hand, secured McConnell’s endorsement for his presidential campaign, as well as his support for changing the state party’s nominating process that allowed Paul to run for president and Senate on the same ballot.

McConnell isn't going to rescind his endorsement of Paul, according to McConnell spokesman Don Stewart, who noted, “Their relationship is a strong one that benefits their state; they disagree on the issue of these counterterrorism tools.”

Stewart also wrote the issue off as presidential politics, noting “there have been senators running for president for as long as anyone can remember.”

Paul's camp has tried downplaying the rift as well, with Paul presidential campaign spokesman Sergio Gor saying the two senators have "a great personal relationship," and said the policy dispute "won't get in the middle of their friendship and mutual respect for each other."

That alliance sustains despite the two senators having been at odds for weeks, with Paul charging that supporters of NSA surveillance, such as McConnell, were countenancing unconstitutional spying on Americans. As Paul forced at least temporary expiration Sunday night, McConnell charged that allowing the expiration would make it easier for terrorists to attack the United States. The feud continued Monday, as McConnell sought to end the standoff and Paul continued to demand amendments.

While many in the Republican Conference have fumed at Paul, Minority Leader Harry Reid has almost gloated from the sidelines.

The Nevada Democrat blamed McConnell for "not having a plan," noting the majority leader had plenty of time to avoid the expiration of the Patriot Act before getting caught at the deadline.

“That is why we are here, staring down the barrel of yet another unnecessary, manufactured crisis that threatens our national security,” he said.

It’s been a “terrible” two weeks for McConnell, said Norman J. Ornstein, a political scientist with the American Enterprise Institute, a right-leaning think tank. McConnell tried and failed to overcome a broad bipartisan coalition that supported the USA Freedom Act, making him look "impotent."

But despite that, it's the complicated nature of Kentucky politics that will keep their alliance intact.

Paul was elected to the Senate in 2010, after having won the Republican primary over McConnell-backed Trey Grayson, earning a libertarian/anti-establishment following in the process. During McConnell's re-election in 2014, Paul endorsed the senior senator and bridged the divide between the two bases enough to beat primary challenger Matt Bevin.

Bevin has since become the party's nominee for governor, showing that the "insurgent" camp that opposed McConnell "hasn't gone away," Ornstein said.

"This is basically part of a set of quids pro quo," he said.

Majority Whip John Cornyn, R-Texas, sought to downplay what has become a party melodrama, saying the two Kentucky senators have a good relationship, despite the sharp disagreement on this issue, which is “normal.”

Cornyn ripped Reid for trying to exploit the split.

“I think there’s a little bit of piling on from the Democrats,” Cornyn said. “I read what Sen. Reid had to say about Sen. McConnell yesterday, which I thought was over the top. This is just part of the rough and tumble, nothing really too unusual.”

Sen. John McCain, R-Ariz., who ran for president twice from the Senate, has no problem voicing his views on Paul, calling him "the worst" candidate the GOP could nominate and at one point objecting to letting him speak for five minutes Sunday night.

After the Patriot Act lapsed Monday, he said he didn’t think there needed to be a conflict between presidential politics and the Senate legislative agenda, and that coordinating with leadership is easy.

“When I ran — twice — I just said: ‘Look, I’m running and I won’t be in the Senate as much as I would otherwise,’” McCain said.

Paul, meanwhile, isn't playing ball and instead took advantage of openings McConnell gave him to single-handedly force a shutdown.

In McCain’s estimation, the problem with the misstep on the Patriot Act/USA Freedom Act stems more from the difference in leadership styles between McConnell and Reid.

“Harry Reid ran the Senate with an iron fist, which means we didn’t have votes, we didn’t have debates,” McCain said. “So Mitch, by opening up the Senate process, obviously there’s going to be different impulses and influences.”